Lighthouse

> Lighthouse analyzes web apps and web pages, collecting modern performance metrics and insights on developer best practices.

Using Lighthouse in Chrome DevTools

Lighthouse is integrated directly into the Chrome Developer Tools, under the "Audits" panel.

Installation: install Chrome.

Run it: open Chrome DevTools, select the Audits panel, and hit "Perform an Audit...".

Using the Chrome extension

Installation: install the extension from the Chrome Web Store.

Run it: follow the extension quick-start guide.

Using the Node CLI

Lighthouse requires Node 6 or later.

Installation:

npm install -g lighthouse
# or use yarn:
# yarn global add lighthouse

Run it: lighthouse https://airhorner.com/

By default, Lighthouse writes the report to an HTML file. You can control the output format by passing flags.

CLI options

$ lighthouse --help

lighthouse 

Logging:
  --verbose  Displays verbose logging                                                                                                      [boolean]
  --quiet    Displays no progress, debug logs or errors                                                                                    [boolean]

Configuration:
  --save-assets                  Save the trace contents & screenshots to disk                                                             [boolean]
  --save-artifacts               Save all gathered artifacts to disk                                                                       [boolean]
  --list-all-audits              Prints a list of all available audits and exits                                                           [boolean]
  --list-trace-categories        Prints a list of all required trace categories and exits                                                  [boolean]
  --additional-trace-categories  Additional categories to capture with the trace (comma-delimited).
  --config-path                  The path to the config JSON.
  --chrome-flags                 Custom flags to pass to Chrome (space-delimited). For a full list of flags, see
                                 https://peter.sh/experiments/chromium-command-line-switches/.

                                 Environment variables:
                                 CHROME_PATH: Explicit path of intended Chrome binary. If set must point to an executable of a build of
                                 Chromium version 54.0 or later. By default, any detected Chrome Canary or Chrome (stable) will be launched.
                                                                                                                                       [default: ""]
  --perf                         Use a performance-test-only configuration                                                                 [boolean]
  --port                         The port to use for the debugging protocol. Use 0 for a random port                                 [default: 9222]
  --hostname                     The hostname to use for the debugging protocol.                                                [default: localhost]
  --max-wait-for-load            The timeout (in milliseconds) to wait before the page is considered done loading and the run should continue.
                                 WARNING: Very high values can lead to large traces and instability                                 [default: 25000]
  --enable-error-reporting       Enables error reporting (prompts once by default, setting this flag will force error reporting to that state).

Output:
  --output       Reporter for the results, supports multiple values                           [choices: "json", "html", "domhtml"] [default: "html"]
  --output-path  The file path to output the results. Use 'stdout' to write to stdout.
                 If using JSON output, default is stdout.
                 If using HTML output, default is a file in the working directory with a name based on the test URL and date.
                 If using multiple outputs, --output-path is ignored.
                 Example: --output-path=./lighthouse-results.html
  --view         Open HTML report in your browser                                                                                          [boolean]

Options:
  --help                        Show help                                                                                                  [boolean]
  --version                     Show version number                                                                                        [boolean]
  --blocked-url-patterns        Block any network requests to the specified URL patterns                                                     [array]
  --disable-storage-reset       Disable clearing the browser cache and other storage APIs before a run                                     [boolean]
  --disable-device-emulation    Disable Nexus 5X emulation                                                                                 [boolean]
  --disable-cpu-throttling      Disable CPU throttling                                                                    [boolean] [default: false]
  --disable-network-throttling  Disable network throttling                                                                                 [boolean]

Examples:
  lighthouse  --view                                                   Opens the HTML report in a browser after the run completes
  lighthouse  --config-path=./myconfig.js                              Runs Lighthouse with your own configuration: custom audits, report
                                                                            generation, etc.
  lighthouse  --output=json --output-path=./report.json --save-assets  Save trace, screenshots, and named JSON report.
  lighthouse  --disable-device-emulation --disable-network-throttling  Disable device emulation
  lighthouse  --chrome-flags="--window-size=412,732"                   Launch Chrome with a specific window size
  lighthouse  --quiet --chrome-flags="--headless"                      Launch Headless Chrome, turn off logging

For more information on Lighthouse, see https://developers.google.com/web/tools/lighthouse/.

Output Examples

lighthouse generates

• ./_.report.html

lighthouse --output json generates

• json output on stdout

lighthouse --output html --output-path ./report.html generates

• ./report.html

NOTE: specifying an output path with multiple formats ignores your specified extension for ALL formats

lighthouse --output json --output html --output-path ./myfile.json generates

• ./myfile.report.json
• ./myfile.report.html

lighthouse --output json --output html generates

• ./_.report.json
• ./_.report.html

lighthouse --output-path=~/mydir/foo.out --save-assets generates

• ~/mydir/foo.report.html
• ~/mydir/foo-0.trace.json
• ~/mydir/foo-0.screenshots.html

lighthouse --output-path=./report.json --output json --save-artifacts generates

• ./report.json
• ./report.artifacts.log

lighthouse --save-artifacts generates

• ./_.report.html
• ./_.artifacts.log

Notes on Error Reporting

The first time you run the CLI you will be prompted with a message asking you if Lighthouse can anonymously report runtime exceptions. The Lighthouse team uses this information to detect new bugs and avoid regressions. Opting out will not affect your ability to use Lighthouse in any way. Learn more.

Viewing a report

Lighthouse can produce a report as JSON or HTML.

HTML report:

Online Viewer

Running Lighthouse with the --output=json flag generates a json dump of the run. You can view this report online by visiting and dragging the file onto the app. You can also use the "Export" button from the top of any Lighthouse HTML report and open the report in the Lighthouse Viewer.

In the Viewer, reports can be shared by clicking the share icon in the top right corner and signing in to GitHub.

> Note: shared reports are stashed as a secret Gist in GitHub, under your account.

Docs & Recipes

Useful documentation, examples, and recipes to get you started.

Docs

• Using Lighthouse programmatically
• Testing a site with authentication
• Testing on a mobile device
• Lighthouse Architecture

Recipes

• gulp - helpful for CI integration
• Custom Audit example - extend Lighthouse, run your own audits

Videos

The session from Google I/O 2017 covers architecture, writing custom audits, GitHub/Travis/CI integration, headless Chrome, and more:

click to watch the video

Develop

Read on for the basics of hacking on Lighthouse. Also see Contributing for detailed information.

Setup

# yarn should be installed first

git clone https://github.com/GoogleChrome/lighthouse

cd lighthouse
yarn
yarn install-all
yarn build-all

# The CLI is authored in TypeScript and requires compilation.
# If you need to make changes to the CLI, run the TS compiler in watch mode:
# cd lighthouse-cli && yarn dev

Run

node lighthouse-cli https://example.com

> Getting started tip: node --inspect --debug-brk lighthouse-cli https://example.com to open up Chrome DevTools and step through the entire app. See Debugging Node.js with Chrome DevTools for more info.

Tests

# lint and test all files
yarn test

# watch for file changes and run tests
#   Requires https://entrproject.org : brew install entr
yarn watch

## run linting, unit, and smoke tests separately
yarn lint
yarn unit
yarn smoke

## run closure compiler (on whitelisted files)
yarn closure
## import your report renderer into devtools-frontend and run devtools closure compiler
yarn compile-devtools

Lighthouse Integrations

This section details projects that have integrated Lighthouse. If you're working on a cool project integrating Lighthouse and would like to be featured here, file an issue to this repo or tweet at us @_____lighthouse

• Calibre - Calibre is a web performance monitoring tool running Lighthouse continuously or on-demand via an API. Test using emulated devices and connection speeds from a number of geographical locations. Set budgets and improve performance with actionable guidelines. Note that Calibre is a paid product with a free 14-day trial.

• HTTPArchive - HTTPArchive tracks how the web is built by crawling 500k pages with Web Page Test, including Lighthouse results, and stores the information in BigQuery where it is publicly available.

• Treo - Treo is Lighthouse as a Service. It provides regression testing, geographical regions, custom networks, and integrations with GitHub & Slack. Treo is a paid product with plans for solo-developers and teams.

• Web Page Test — An open source tool for measuring and analyzing the performance of web pages on real devices. Users can choose to produce a Lighthouse report alongside the analysis of WebPageTest results.

Related Projects

• webpack-lighthouse-plugin - run Lighthouse from a Webpack build.
• lighthouse-mocha-example - gather performance metrics via Lighthouse and tests them in Mocha
• pwmetrics - gather performance metrics
• lighthouse-hue - set the color of Philips Hue lights based on a Lighthouse score
  • lighthouse-magic-light set the color of the MagicLight Bluetooth Smart Light Bulb based on Lighthouse score
• lighthouse-batch - run Lighthouse over a number of sites and generate a summary of their metrics/scores.
• lighthouse-cron - Cron multiple batch Lighthouse audits and emit results for sending to remote server.
• lightcrawler - Crawl a website and run each page found through Lighthouse.

FAQ

How does Lighthouse work?

See Lighthouse Architecture.

Can I configure the lighthouse run?

Yes! Details in Lighthouse configuration.

How does Lighthouse use network throttling, and how can I make it better?

Good question. Network and CPU throttling are applied by default in a Lighthouse run. The network attempts to emulate 3G and the CPU is slowed down 4x from your machine's default speed. If you prefer to run Lighthouse without throttling, you'll have to use the CLI and disable it with the --disable-* flags mentioned above.

Read more in our guide to network throttling.

Are results sent to a remote server?

Nope. Lighthouse runs locally, auditing a page using a local version of the Chrome browser installed the machine. Report results are never processed or beaconed to a remote server.

How do I author custom audits to extend Lighthouse?

> Tip: see Lighthouse Architecture for more information on terminology and architecture.

Lighthouse can be extended to run custom audits and gatherers that you author. This is great if you're already tracking performance metrics in your site and want to surface those metrics within a Lighthouse report.

If you're interested in running your own custom audits, check out our Custom Audit Example over in recipes.

How do I contribute?

We'd love help writing audits, fixing bugs, and making the tool more useful! See Contributing to get started.

Lighthouse, ˈlītˌhous (n): a tower or other structure tool containing a beacon light to warn or guide ships at sea developers.